1. Field of the Invention
The present invention relates to a method for high-speed Ethernet channel impairment enhancement and apparatus using the same.
2. Description of the Related Art
Among high data rate transmission systems, high-speed Ethernet local area networks (LANs), 100 BASE-TX Ethernet and 1000 Base TX Ethernet using category-5 or above 5 copper wire are all being developed rapidly. The 1000 Base TX Ethernet, also called gigabit Ethernet, uses four unshielded twisted pairs of wires to transmit data at 1 Gb/second. In the case of using Ethernet to communicate in a communication network, an extremely low bit error rate (BER) is required to transmit encoded data. However, in a communication system with a number of unshielded twisted pairs of wires and transceivers, issues of channel impairment, such as fading, near-end cross talk, echo, and noise, are encountered frequently, which causes unclean signals and affects coding.
FIG. 1 shows a block diagram of a typical communication system 10. The communication system 10 comprises a plurality of transceivers 12, a plurality of hybrids 14, and a plurality of communication lines 16 including four unshielded twisted pairs of wires 18. Referring to FIG. 1, the transceivers 12 comprise a transmitter TX and a receiver RX. The hybrids are positioned between each transceiver 12 and its associated unshielded twisted pair 18. The hybrids 14 control access to the communication lines 16, thereby allowing for full-duplex bidirectional operation between the transceivers 12 at each end of the communication lines 16. The hybrids 14 are also used to isolate the transmitter and receiver associated with the transceiver.
A signal NEXT in FIG. 1 is a channel impairment signal, which results from capacitive coupling of the signals from the near-end transmitters TX to the input of the receivers RX. The NEXT impairment signals received by the receiver RX in a transceiver A are shown in FIG. 1, and the crosstalk signals are generated by transceivers B, C, and D. Similarly, because of the bidirectional nature of the communication systems, an echo impairment signal ECHO is produced by each transmitter on the receiver contained within the same transceiver as shown in FIG. 1. To reduce the BER when communicating over the communication systems, the transceiver requires adding an echo canceller and a near-end cross talk canceller to suppress the impairment signals.
Assume that a device with the transceivers shown in FIG. 1 is a master device that is coupled to a slave device. First, the master device sends an idle sequence to the slave device, and trains its echo canceller and near-end cross talk canceller before the slave device sends a signal. The cancellation filter coefficients of the echo canceller and near-end cross talk canceller are used to obtain impulse responses of the echo signal and the near-end cross talk signal at this stage so as to eliminate the impairment signals. However, since the timing between the transmitter TX and the receivers RX are not exactly the same, the output signals of the echo canceller and the near-end cross talk canceller have phase differences between the ideal echo and near-end cross talk canceller, therefore, such method cannot suppress the echo and the near-end cross talk problem efficiently. Accordingly, it is desirable to provide a method for enhancing Ethernet channel impairment and apparatus using the same for eliminating noise problems including echo and near-end cross talk so as to reduce the BER and improve the transmission quality of high-speed Ethernet communications.